How to use Sql Union? Smart way to combine sql results.
This sql command is a simple concept. It combines two or more sql results. Each subsequent sql result is appended to the previous result.
Things to remember:
- each sql must have the same number of columns.
- data types must be compatible
- the column's order must be the same.
The clause ALL that is added to Sql Union is to avoid elimination of duplicate entries. That is, use UNION only if you want the program to select distinct values during the merge, and use UNION ALL if you want to select all data.The Syntax
Let's use the following simple tables to clarify.
Please note ID=7 appears in Tbl_A and Tbl_B. Since Sql Union only selects distinct rows, it elimates duplicate and shows only one. Notice that the result is sorted.
Compare with this one.
One more thing, notice the row order has not changed either. This Sql Union with ALL keywrod runs faster
Sql Create Database
Use this to create a database.
Sql Create Table
This Sql Create Table will be used very often throughout the tutorial. It is used to create a table, in our case, mainly to create sample tables.
Sql Alter Table
Used less often, but it is very handy to know this command. With this you can basically edit a table structure.
Sql Drop Table
Used to delete a table, not just the content. This command is also used very often during the tutorial. So, you need to master this too.
To add rows to a table, you use Sql Insert command. There are two methods, one is with the VALUES keyword and second is with a SELECT statement.
To change existing rows, you use Sql Update command. You can use it to change values in a single row, groups of rows or all rows. You can also update a table based on values in other tables.
To remove rows, you use Sql Delete command. You can delete one rows, group of rows or all rows. You can also delete rows based on values in other tables.
The core of Sql, selecting data from table.
Eliminating duplicate values in the output.
Conditionally selecting rows from table.
Pattern searching for conditions in Where or Having clause
Added to conditions to show results between two values.
It enables us to specify multiple values, either as a list or a subquery.
Sql And Or
Connecting two or more conditions in the Where or Having clause.
Counting number of rows.
Getting the sum of a field
This function will return the highest value.
This function will return the lowest value.
This function will return the average value.
Sql Order By
Sorting the output
Sql Group By
Grouping rows into sets.
To filter the result of aggregation
Advanced Sql Tutorial
Sql Inner Join
Use Sql Join to retrieve data from more than one table in just one Select statement.
Sql Outer Join
An Sql outer join shows the join, and all the rows that do not qualify.
Sql Self Join
A join that compares values within a single table.
A nested Sql Select inside the WHERE clause of another Sql Select statement.
Return from Sql Union to Advanced Sql Tutorial
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